1. Field of the Invention
This invention relates to a drainage pump, in particular, to be coupled to a sump tank receiving drain Water in an air conditioner to discharge it to the exterior.
2. Description of the Prior Art
There are known drainage pumps for use with a sump tank of an air conditioner, such as those disclosed in Japanese Utility Model Post-Examination Publication Hei 3-35915 and Japanese Utility Model Laid-Open Publication Hei 6-60795.
Such a drain pump comprises a pump body which defines an interior chamber with a curved inside surface configured to gradually increase in inner diameter and has an inlet at a location with a smaller diameter and an outlet at a location with a larger diameter; and a rotary vane which can rotate in the pump body while keeping a distance from the inside surface of the pump body.
When the liquid reaches a level touching an end of the rotary vane, an electric motor is activated to rotate the rotary vane in a given direction. Since the outer diameter of the rotary vane and the inner diameter of the pump body progressively increase upwardly, larger and larger centrifugal force acts on the liquid as the liquid moves upwardly in the pump body. Thus a predetermined lift is maintained.
The prior art disclosed in Publication 6-60795, referred to above, uses a rotary vane with four or six blades radially extending from the rotational axle of the pump. Every other one of the blades has a shape corresponding to the upper half of its adjacent blade.
Japanese Utility Model Laid-Open Publication Hei 5-38385 discloses a drainage pump using a vane with curved small-radial blades under four rotary blades.
Similarly, Japanese Utility Model Laid-Open Publication Hei 6-67887 discloses a drainage pump using a vane with two or four small-radial blades under two or four large-radial blades.
FIGS. 41A and 41B show an arrangement of drainage pump using four large-radial blades and four small-radial blades, for example.
The drainage pump 1 comprises a pump body 10 topped with a cover 30. The pump body 10 has a pump chamber 12 defined by a cylindrical housing 11, an inlet conduit 14 forming an inlet 15 at the bottom center of the pump chamber 12, and an outlet conduit 16 horizontally extending from the pump chamber 12 and forming an outlet 17.
A rotary vane 40 mounted on the output shaft of a motor (not shown) comprises a shaft 42, four large-radial blades 44 accommodated in the pump chamber 12 connected to the shaft 42, and four small-radial blades 46 disposed under the large-radial blades 44 and accommodated in the inlet conduit 14. Provided between the shaft 42 of the vane 40 and the cover 30 is a through hole 32 covered at its upper end by a sheet 34 attached to the rotary shaft to prevent splashes of water to the exterior.
FIG. 41A is a top view of the vane 40 rotating in the pump chamber 12b in the arrow-marked direction during drainage of water.
For the experimental purpose, the pump body and the cover were made of a transparent resin, and a process of drainage by the rotary vane 40 was observed. FIG. 41A shows a result of the observation which reveals that bubbles labelled G.sub.1 generate around the large-radial blades 44 of the rotary vane 40.
These bubbles hit the blades, inside wall surface of the pump chamber, inside wall surface of the inlet conduit, and so forth, and such collisions make a noise, vibrations, etc.